The present invention relates to hot and cold packs. More particularly, it relates to a three-compartment, instant hot or cold, reusable cold pack for transferring heat to or from an object.
One type of hot or cold pack typically includes a rupturable container having a first chemical therein. A second chemical is positioned adjacent the rupturable container with the rupturable container preventing contact between the two chemicals. Upon rupture, the first and second chemicals mix to liberate or absorb heat and thereby produce the desired heating or cooling effect. One such pack is disclosed in U.S. Pat. No. 3,763,622.
Another type of a thermal pack is disclosed in U.S. Pat. No. 3,874,504. In one embodiment, an outer pouch slidably receives a sealed intermediate pouch containing the separated, thermally-active ingredients. When the pack is squeezed, a membrane separating the ingredients is ruptured and the heating or cooling effect realized. In another embodiment, different ingredients are premixed in an envelope to form a gel. The gel pack is placed in a refrigerator to lower its temperature prior to application to an object to be cooled.
The prior art hot or cold packs have been one of these two types. They have either been designed to provide an instant heating or cooling effect upon the mixing of two or more chemicals, or they have relied upon an outside source of heating or cooling. The latter form of packs have typically been gel packs. They have been cooled in a refrigerator to achieve the desired effect.
One advantage of the gel packs over the instant packs is their flexibility or moldability even when frozen. This is known to facilitate their use on curved surfaces. U.S. Pat. No. 3,545,230 discloses a number of insoluble hydrophylic gels which are said to be useful in cold packs. Packs made from the gels disclosed are said to be moldable even when frozen to conform to various geometric shapes. The packs are used by first freezing them and then applying them to the area to be cooled.
One such gel pack is marketed by Minnesota Mining and Manufacturing Company, 3M Center, St. Paul, Minn. 55144, under the trademark "COLD COMFORT". It is comprised of 70 weight percent water, 25 weight percent propylene glycol and 5 weight percent hydroxypropyl methylcellulose, type K15MDGS, as purchased from Dow Chemical Company, Midland, Mich. 48640 under the trademark "METHOCEL". The gel is made by first wetting the hydroxypropyl methylcellulose with the propylene glycol. The water is next added to form the finished gel.
U.S. Pat. No. 3,804,077 discloses an instant hot or cold pack which also forms a gel. The pack includes a first sealed compartment containing particles of a first material such as calcium chloride or ammonium nitrate. Particles of a suitable material such as a starch are mixed with the particles of the first material in the first compartment. The first compartment is disposed within a sealed second compartment containing a second material such as water and having rupturable properties. When the second compartment is ruptured, the materials in the two compartments are said to become mixed. The ammonium nitrate in the first compartment reacts endothermally with the water in the second compartment. The starch is said to form a gel and impede the movements of the materials in the pack. The inclusion of the starch in the pack is believed to be disadvantageous to the chemical reaction between the materials in the pack since it slows the rate at which the chemical reaction occurs and thus reduces the ultimate temperature change achievable. The starch is said to be advantageous since it is said to be compatible with the other materials in the pack and does not react chemically with any of these other materials in the pack to prevent these materials from reacting chemically with each other to produce the cooling effect. If it were frozen, it is believed the pack would be hard and inflexible.
The prior instant hot and cold packs have been able to provide heating and cooling effects at ambient temperatures, but they have been inadequate when frozen due to their hardness and inflexibility. Reusable gel packs have been soft and moldable when frozen, but they have been useless without the accessibility of a refrigerator to create the cooling effect. Never before have the advantages of the two types of packs been combined.